Tar sands (also known as "heavy oil sands" or "bituminous sand") are believed to be formed by infiltration of petroleum into porous sand near the Earth's surface. Tar sands are crude oil deposits that are substantially heavier (more viscous) than other crude oils. Tar sands are bitumen (a substance with the consistency of molasses that comprises up to 18% of the oil sands), which is a liquid-solid organic material, such as tar, asphalt, or heavy oil. This heavier crude oil has lost much of its lighter fraction of its original petroleum due to volatilization or oxidation. Often times, heavy oil is mixed with sand, hence, the name "heavy oil sands"; although, it does not necessarily have to be mixed with sand. Some tar sands occur in limestone or clay.
Tar sands are generally of interest to geologists because they are a potentially huge source of petroleum. Crude oil (or tar) can be separated from enclosing rock with hot water or steam. Heavy crude oil then can be chemically upgraded into a lighter crude oil by "cracking" and/or "hydrogenation", which is used commercially. Tar sands require more processing than conventional crude oil and are therefore more expensive to utilize. Tar sands occur naturally throughout the world, including in Alberta, Canada, Argentina and Utah. Generally, tar sands are used to make "synthetic" oil and other petroleum products, although the processes for doing so are generally presently considered prohibitively expensive.
Other uses for tar sands have been contemplated. For instance, in Utah, native tar sands have been mined and placed on roads by trucks and graders to produce an asphalt road surface. Furthermore, several companies have tried, without great success, to produce a hot asphalt with native tar sand. Reportedly, ninety-six percent of all paved roads and streets in the U.S.--almost two million miles--are surfaced with asphalt, and to incorporate native tar sand into a hot asphalt production process would be an improvement in the art.
Unfortunately, using tar sand in a hot asphalt process has had several problems and drawbacks associated with it. For instance, with the prior art methods, excessive smoking occurs, the tar sands burn, and the tar sands can combust while in a drum mixer used in an asphalt-producing process. Furthermore, the material adheres to belting, and plugs feed bins and the drum mixer used in the process. It has also been difficult to attain a consistent feed when using tar sands in the asphalt mix.
It would be an improvement in the art if a relatively simple process existed for successfully incorporating tar sands into a hot asphalt process.